A variety of industrial as well as non-industrial applications use fuel burning boilers, typically for converting chemical energy into thermal energy by burning one of various types of fuels, such as coal, gas, oil, waste material, etc. An exemplary use of fuel burning boilers is in thermal power generators, wherein fuel burning boilers are used to generate steam from water traveling through a number of pipes and tubes in the boiler and the steam is then used to generate electricity in one or more turbines. The output of a thermal power generator is a function of the amount of heat generated in a boiler, wherein the amount of heat is determined by the amount of fuel that can be burned per hour, etc. Additionally, the output of the thermal power generator may also be dependent upon the heat transfer efficiency of the boiler used to burn the fuel.
Burning of certain types of fuel, such as coal, oil, waste material, etc., generates a substantial amount of soot, slag, ash and other deposits (generally referred to as “soot”) on various surfaces in the boilers, including the inner walls of the boiler as well as on the exterior walls of the tubes carrying water through the boiler. The soot deposited in the boiler has various deleterious effects on the rate of heat transferred from the boiler to the water, and thus on the efficiency of any system using such boilers. It is necessary to address the problem of soot in fuel burning boilers that burn coal, oil, and other such fuels that generate soot in order to maintain a desired efficiency within the boiler. While not all fuel burning boilers generate soot, for the remainder of this patent, the term “fuel burning boilers” is used to refer to those boilers that generate soot.
Various solutions have been developed to address the problems caused by the generation and presence of soot deposits in boilers of fuel burning boilers. One approach is the use of soot blowers to remove soot encrustations accumulated on boiler surfaces through the creation of mechanical and thermal shock. Another approach is to use various types of soot blowers to spray cleaning materials through nozzles, which are located on the gas side of the boiler walls and/or on other heat exchange surfaces, where such soot blowers use any of the various media such as saturated steam, superheated steam, compressed air, water, etc., for removing soot from the boilers.
Soot blowing affects the efficiency and the expense of operating a fuel burning boiler. For example, if inadequate soot blowing is applied in a boiler, it results in excessive soot deposits on the surfaces of various steam carrying pipes and therefore in lower heat transfer rates. In some cases, inadequate soot blowing may result in “permanent fouling” within fuel burning boilers, meaning that soot deposits in the boiler are so excessive that such deposits cannot be removed by any additional soot blowing. In such a case, forced outage of the boiler operation may be required to fix the problem of excessive soot deposits, and boiler maintenance personnel may have to manually remove the soot deposits using hammers and chisels. Such forced outages are not only expensive, but also disruptive for the systems using such fuel burning boilers.
On the other hand, excessive soot blowing in fuel burning boilers may result in increased energy cost to operate the soot blowers, wastage of steam that could otherwise be used to operate turbines, etc. Excessive soot blowing may also be linked to boiler wall tube thinning, tube leaks, etc., which may cause forced outages of boiler use. Therefore, the soot blowing process needs to be carefully controlled.
Historically, soot blowing in utility boilers has been mostly an ad hoc practice, generally relying on a boiler operator's judgment. Such an ad hoc approach produces very inconsistent results. Therefore, it is important to manage the process of soot blowing more effectively and in a manner so that the efficiency of boiler operations is maximized and the cost associated with the soot blowing operations is minimized.
One popular method used for determining cleanliness of a boiler section and to control soot blowing operations is a first principle based method, which requires measurements of flue gas temperature and steam temperature at the boiler section inlets and outlets. However, because direct measurements of flue gas temperatures are not always available, the flue gas temperatures are often backward calculated at multiple points along the path of the flue gas, starting from the flue gas temperatures measured at an air heater outlet. This method is quite sensitive to disturbances and variations in air heater outlet flue gas temperatures, often resulting in incorrect results. Moreover, this method is a steady state method, and therefore does not work well in transient processes generally encountered in various boiler sections.
Another popular method used for determining cleanliness of a boiler section of a fuel burning boiler and to control soot blowing operations in a fuel burning boiler is an empirical model based method, which relies on an empirical model such as a neural network model, a polynomial fit model, etc. The empirical model based method generally requires a large quantity of empirical data related to a number of parameters, such as the fuel flow rate, the air flow rate, the air temperature, the water/steam temperature, the burner tilt, etc. Unfortunately the large amount of data makes the data collection process tedious, and prone to high amount of errors in data collection.